Line switch part snow melting device

ABSTRACT

A thawing device for railway track points is constituted by connecting a heating coil ( 1   a ) wound around a floor plate ( 2 ) for heating the floor plate ( 2 ) by induction to an inverter device ( 5 ) for supplying high-frequency current to the heating coil ( 1   a ), via a connection cable ( 4 ); and providing a protection against magnetism ( 9, 10   a   -10   c   , 11   a   -11   c    , 12   a   , 12   b ) about the periphery of the heating coil ( 1   a ) and the connection cable ( 4 ).

TECHNICAL FIELD

The present invention relates to a thawing device for railway trackpoints for preventing failures in points changing due to snow or icingat the points sections of railway tracks.

BACKGROUND ART

Conventional types of thawing device for railway track points include,as a device for use in regions having large amounts of snow, a hot airblower type of thawing device, wherein kerosene or the like is burnt andhot air generated thereby is blown via a duct onto the points sections.Furthermore, as a device for use in regions having small amounts ofsnow, there is an electric heater type thawing device, wherein electricheaters are placed on the main rails and the side regions of floorplates, thereby heating the points sections.

However, these conventional thawing devices have following problems% inthe case of the hot air blower type of thawing device, although thethawing capacity is excellent, there have been problems in that theheating efficiency is poor and hence fuel expenses are high, there is arisk of accidental fire, and disassembly and maintenance must be carriedout in the season when the device is out of use. In the case of theelectric heater type thawing device, there have been problems in thatthe thawing capacity is low, the rate of temperature increase is show,and ease of installation is poor, given that a special floor plate isused, and the like.

In order to increase the heating efficiency, it may be considered to usehigh-frequency current, but this brings a risk that the magnetic fluxcreated by the high-frequency current may affect other devices.

Consequently, an object of the present invention is to provide a thawingdevice for railway track points sections which solves theabove-mentioned problems by lowering running costs by means of highlyefficient heating, and which secures safety by reducing the effects onother devices of the magnetic flux caused by the high-frequency current.

DISCLOSURE OF THE INVENTION

A thawing device for railway track points according to a first aspect ofthe present invention is characterized by including: a heating coilwound around a floor plate for heating the floor plate by induction; andan inverter device for supplying high-frequency current to the heatingcoil. By adopting this construction, the heating coil is wound aroundthe floor plate and the heating surface area is increased, and hence thefloor plate is heated at high-power with a high-frequency current, and agood effect in preventing ice formation on the floor plate and/or railsis obtained by thermal conduction from the floor plate to a main railand tongue rails. Moreover, since the heating coil does not projectsignificantly beyond a sleeper, it does not obstruct track maintenancework, and does not require detachment outside of the snow season.

In the aforementioned construction, it is preferred that the heatingcoil is wound through one or more turns in contact with the side face orthe lower face of the floor plate. Thereby, the heating surface area isincreased further, floor plate induction heating is performed athigh-power, and a highly effective thawing capacity is achieved.

Further, it is preferred that a portion of the heating coil is wound incontact with the upper face of the floor plate. Thereby, the heatingcoil can be wound around the floor plate even in cases where the floorplates of the left and right-hand rails are connected, for example, atthe front end portion of a railway points, or in cases where the floorplate is long.

A thawing device for railway track points according to a second aspectof the invention is characterized by including:

a heating coil wound around a floor plate for heating the floor plate byinduction; an inverter device for supplying high-frequency current tothe heating coil; and a protection against coil magnetism for preventingmagnetic flux of the heating coil from leaking. By adopting thisconstruction, leakage of magnetic flux from the high-frequency magneticfield generated by the heating coil is reduced, thereby reducing theeffects of high-frequency noise on other devices.

In the aforementioned construction, it is preferred that the protectionagainst coil magnetism is constituted by a cover made of a materialhaving high resistivity and high magnetic permeability, which covers theperiphery of the heating coil wound around the floor plate. Thereby,leakage of magnetic flux of the heating coil is prevented, and theeffects of high-frequency noise on other devices is reduced, whilst atthe same time suppressing any heating by induction of the coil magnetismprevention means itself, due to the magnetic flux.

Alternatively, the protection against coil magnetism may be constitutedby first closed loop conductors disposed about the outer circumferenceof a single heating coil or a plurality of heating coils wound aroundthe floor plates, and second closed loop conductors disposed around theperiphery of the first closed loop conductors. Thereby, an eddy currentwhich cancels out magnetic flux leaking from the first closed loop isinduced in the second closed loop conductors, and the area peripheral tothe heating coils is protected against magnetism, and the effects ofhigh-frequency noise on other devices are reduced.

A thawing device for railway track points according to a third aspect ofthe invention is characterized in that a plurality of heating coilswound around floor plates for heating the floor plates by induction areconnected in series by means of a feeder cable, these heating coils areconnected by means of connection cables with a single inverter devicefor supplying high-frequency current to the heating coils, and aprotection against cable magnetism is provided for preventing magneticflux of the cables from leaking. By adopting this construction leakageof high-frequency magnetic flux generated by the cables is reduced,thereby reducing the effects of high-frequency noise on other devices.

In the aforementioned construction, it is preferred that the protectionagainst cable magnetism is constituted by twisting the supply or returnconnection cables from the inverter device to the heating coils, and thefeeder cable. Thereby, the magnetic fluxes induced by the high-frequencycurrent in the supply and return cables cancel out mutually, and thearea peripheral to the cables is protected against magnetism and theeffects of high-frequency noise on other devices are reduced.

Alternatively, the protection against cable magnetism ay be constitutedby covers which cover the periphery of the supply and return connectioncables from the inverter device to the heating coils,-and the feedercable, and which are connected in a closed loop in the vicinity of theheating coils and the inverter device. Thereby, an eddy current whichcancels out magnetic flux inside the closed loop having leaked from theconnection cables is induced in the covers of the closed loop, and thearea peripheral to the cables is protected against magnetism and theeffects of high-frequency noise on other devices are reduced.

Alternatively, the protection against cable magnetism may be constitutedby superposing coils wherein portions of the supply and returnconnection cables are wound respectively in the same direction, to thesame diameter, and through the same number of turns. Thereby, themagnetic fluxes induced by the high-frequency current in the supply andreturn connection cables cancel out mutually, and the area peripheral tothe cables is protected against magnetism and the effects ofhigh-frequency noise on other devices are reduced.

A thawing device for railway track points according to a fourth aspectof the Invention is characterized by including:

a heating coil for heating a floor plate by induction; an inverterdevice for supplying high-frequency current to the heating coil; a traindetecting device for detecting the approach of a train to a pointssection; and an inverter controller for outputting a signal to theinverter device, the signal for either reducing or interrupting thesupply of high-frequency current to the heating coil for a prescribedperiod of time after the approach of a train has been detected by thetrain detecting device. By adopting this construction, the supply ofhigh-frequency current from the inverter device to the heating coil iseither reduced or interrupted for a prescribed period of time after theapproach of a train is detected. Thereby, the effects of thehigh-frequency noise on the high-precision equipment of the train arereduced, when the train is passing over the points section.

In the aforementioned construction, it is preferred that the traindetecting device includes a magnetic field detector for converting anelectrical signal into a magnetic flux and detecting changes in magneticfield caused by the approach of a train. In the magnetic flux generatedby the coil or the like of the magnetic field detector, the magneticresistance will change if a portion of a trains namely, a train wheel,is present. By detecting the changes in impedance and changes in signalcurrent corresponding to this change, the approach of a train isdetected, whereupon, for a prescribed period of time, the supply ofhigh-frequency current to the heating coil is reduced or interrupted,thereby reducing the effects of high-frequency noise on thehigh-precision equipment of a train when the train is passing over apoints section.

Alternatively, the train detecting device may be constituted by a signaltransmitter for inputting a track path signal indicating whether a shortcircuit is caused between the left and right-hand rails by an axle of atrain within a prescribed sections and transmitting a trainpresent/absent signal; and a signal receiver for receiving thetransmitted train present/absent signal. When a train enters theprescribed section and the left and right-hand rails are shorted by thetrain axle, a train present signal is output from the signal transmitterto the signal receiver, whereby the train detecting device detects thata train is passing through, or is halted in, the points section.Whereupon, the supply of high-frequency current to the heating coil isreduced or interrupted for a prescribed period of time, and hence theeffects of high-frequency noise on the high-precision equipment of atrain is reduced when the train is passing through a points section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B show a thawing device for railway track pointsaccording to a first embodiment of the present invention: FIG. 1A is afront view and FIG. 1B is a plan view;

FIG. 2A and FIG. 2B show a thawing device for railway track pointsaccording to a second embodiment of the invention: FIG. 2A is a frontview and FIG. 2B is a plan view;

FIG. 3A and FIG. 3B show a mode of installation of a thawing device forrailway track points according to a third embodiment of the invention:FIG. 3A is a front view and FIG. 3B is a plan view;

FIG. 4A to FIG. 4C show a thawing device for railway track pointsaccording to a fourth embodiment of the invention: FIG. 4A is a frontview, FIG. 4B is a plan view, and FIG. 4C is an enlarged sectional viewof the portion indicated by IVC in FIG. 4B;

FIG. 5. is a diagram illustrating a thawing device for railway trackpoints according to a fifth embodiment to the invention;

FIG. 6 is a diagram illustrating a thawing device for railway trackpoints according to a sixth embodiment of the invention;

FIG. 7 is a diagram illustrating a thawing device for railway trackpoints according to a seventh embodiment of the invention;

FIG. 8 is a diagram illustrating a thawing device for railway trackpoints according to an eighth embodiment of the invention;

FIG. 9 FIG. 9C show a thawing device for railway track points accordingto a ninth embodiment of the invention: FIG. 9A is a front view, FIG. 9Bis a plan view, and FIG. 9C is an illustrative diagram of the railwaytracks;

FIG. 10A and FIG. 10B show a thawing device for railway track pointsaccording to a tenth embodiment of the invention: FIG. 10A is a frontview and FIG. 103 is a detailed view of the portion indicated by XB inFIG. 10A; and

FIG. 11 is a diagram showing a thawing device for railway track pointsaccording to an eleventh embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be described below withreference to FIG. 1A to FIG. 11.

(First Embodiment)

A thawing device for railway track points according to a firstembodiment of the present invention is described with reference to FIGS.1A and 1B. Numeral 1 a denotes a heating coil which is wound along theside face of a floor plate 2 and accommodated inside a heating coil case1 c. The heating coil 1 a is connected by a connection cable 4 to aninverter device 5 which supplies high-frequency current from acommercial power source 3. When a high-frequency current is supplied tothe heating coil 1 a, a high-frequency magnetic field is generatedtherein, and the floor plate 2 is induction heated by thishigh-frequency magnetic field. Heat generated in the floor plate 2 istransferred to a main rail 6 and a tongue rail 7, thereby raising thetemperature of these rails 6 and 7, consequently, any snow or icepresent on the floor plate 2 or rails 6 and 7 is caused to melt, andhence points changing failures are prevented. Furthermore, since theheating coil 1 a is wound once or more times around the side face of thefloor plate 2, induction heating is performed at high-power, and a goodeffect in preventing ice formation is achieved by thermal conduction tothe rails 6 and 7. Additionally, since the heating coil 1 a does notproject significantly beyond a railway sleeper 8, it does not interferewith track maintenance tasks such as ballast packing or the like, anddoes not need to be removed outside of the snow season.

(Second Embodiment)

A second embodiment of the present invention is described with referenceto FIGS. 2A and 2B. In this embodiment, the thawing device for railwaytrack points is constituted by winding the heating coil 1 a accommodatedin the heating coil casing 1 c, one or more times in contact with thelower face of the floor plate 2. Besides this, the construction is thesame as that in the first embodiment, and high-frequency current issupplied to the heating coil 1 a from the commercial power source 3, viathe inverter device 5. The heating coil 1 a generates a high-frequencymagnetic field due to the high-frequency current supplied thereto, andthe floor plate 2 is induction heated by the magnetic field. Heatgenerated in the floor plate 2 is transferred to the main rail 6 andtongue rail 7, thereby raising the temperature of these rails 6 and 7.Consequently, any snow or ice present on the floor plate 2 or the rails6 and 7 is caused to melt, thereby preventing points changing failures.Furthermore, since the heating coil 1 a is wound one or more times incontact with the lower face of the floor plate 2, induction heating isperformed at high-power, and a good effect in preventing ice formationis achieved by thermal conduction to the rails 6 and 7. Additionally,since the heating coil 1 a does not project significantly beyond therailway sleeper 8, it does not interfere with track maintenance taskssuch as ballast packing or the like, and does not need to be removedoutside of the snow season.

(Third Embodiment)

A third embodiment of the present invention is described with referenceto FIGS. 3A and 3B. In this embodiment, the thawing device for railwaytrack points is constituted ouch that the heating coil 1 a is woundalong the side face of the floor plate 2, but at a position which doesnot interfere with the opening and closing operation of the tongue rail7, a portion P of the heating coil 1 a is wound in contact with theupper surface of the floor plate 2. By adopting this construction, it ispossible to wind the heating coil 1 a around the floor plate 2, even incases where the floor plates 2 of the left and right-hand rails 7 areconnected at the front end portion of a railway track points section, orwhere the floor plate 2 is long.

(Fourth Embodiment)

A fourth embodiment of the present invention is described with referenceto FIGS. 4A to 4C. In this embodiment, the periphery of the heating coil1 a wound along the side face of the floor plate 2 is covered by aprotection against coil magnetism 9, which prevents the magnetic flux ofthe heating coil 1 a from leaking. The protection against coil magnetism9 is made from a material having high resistivity and high magneticpermeability, such as ferrite, and forms a closed magnetic circuit withthe side face of the floor plate 2, whereby leakage of magnetic fluxfrom the high-frequency magnetic field generated in the heating coil 1 ais reduced, and induction heating of the protection against coilmagnetism 9 itself is suppressed. Besides this, the basic constructionis similar to that of the various embodiments described above, heatgenerated in the floor plate 2 being transferred to the main rail 6 andtongue rail 7, thereby causing snow or ice present on the floor plate 2or rails 6 and 7 to melt and hence preventing failures in pointschanging.

(Fifth Embodiment),

A fifth embodiment of the invention is described with reference to FIG.5. In this embodiment, a first closed loop conductor 10 a is disposedabout the outer circumference of a first heating coil 1 a positionedabout the periphery of a first floor plate 2 a, a second closed loopconductor 10 b is disposed about the outer circumference of a secondheating coil 1 b positioned about the periphery of a second floor plate2 b, and a third closed loop conductor 10 c is disposed about the outercircumferences of these two closed loop conductors 10 a and 10 b, aprotection against coil magnetism being constituted by these conductors10 a, 10 b, and 10 c. By adopting this construction, an eddy current isinduced in the third closed loop conductor 10 c so as to cancel out anymagnetic flux in the first and second closed loop conductors 1 a and 10b which has leaked from the first and second heating coils 1 a and 1 b,and therefore magnetic flux of the heating coils 1 a and 1 b isprevented from leaking. Incidentally, numeral 4 a in FIG. 5 denotes aconnection cable which connects the heating coils 1 a and 1 b to theinverter device 5, and numeral 4 b is a feeder cable.

(Sixth Embodiment)

A sixth embodiment of the invention is described with reference to FIG.6. In this embodiment, similarly to the fifth embodiment, a protectionagainst coil magnetism is constituted by respectively disposingconductors 10 a to 10 c about the circumferences of the heating coils 1a and 1 b wound respectively around the floor plates 2 a and 2 b, inaddition to which a protection against magnetism is also provided forthe cables. More specifically, the heating coils 1 a and 1 b areconnected in series by means of the feeder cable 4 b, and furthermore, aprotection against cable magnetism is constituted by twisting the supplyconnection cable and the return connection cable 4 a and 4 a, and alsothe feeder cable 4 b, along which the high-frequency current passes. Byadopting this construction, the high-frequency current flows in oppositedirections in the supply and return cables, and the high-frequencymagnetic fields generated in the twisted connection cables 4 a and 4 aalso act in opposite directions, thereby cancelling each other out, andhence preventing leakage of magnetic flux of the cables.

(Seventh Embodiment)

A seventh embodiment of the invention is described with reference toFIG. 7. In this embodiment, the heating coils la and 1 b woundrespectively along the floor plates 2 a and 2 b are connected in seriesvia the feeder cable 4 b and two connection cables 4 a and 4 c, to thesingle inverter device 5. A protection against cable magnetism isconstituted by covering these three cables 4 a, 4 b, and 4 c by means ofshields (cable magnetism-proof covers) 11 a, 11 b, and 11 c. The shields11 a, 11 b, and 11 c are connected at three locations in the vicinity ofthe heating coils 1 a and 1 b and in the vicinity of the inverter device5, in such a manner that they form a closed loop. By adopting thisconstruction, an eddy current is induced in the shields 11 a, 11 b, and11 c forming the closed loop which cancels out any magnetic flux insidethe closed loop having leaked from the cables 4 a, 4 b, and 4 c, therebypreventing magnetic flux of the cables from leaking.

(Eighth Embodiment)

An eighth embodiment of the invention is described with reference toFIG. 8. In this embodiment, the heating coils 1 a and 1 b woundrespectively along the floor plates 2 a and 2 b are connected in seriesby means of the feeder cable 4 b and two connection cables 4 a and 4 c,to the single inverter device 5. A protection against cable magnetism isconstituted by superposing two coils 12 a and 12 b which are formed bywinding respective portions of the two connection cables 4 a and 4 c inthe same direction, to the same diameter, and by the same number ofturns. By adopting this construction, the magnetic fluxes induced by thehigh-frequency current in the supply and return connection cables canceleach other out, thereby preventing magnetic flux of the cables fromleaking.

(Ninth Embodiment)

A ninth embodiment of the invention is described with reference to FIGS.9A to 9C. In this embodiment, similarly to the first embodiment, ahigh-frequency current is supplied by the inverter device 5 to theheating coil 1 a (numeral 1 c indicates the casing inside which the coilis accommodated) wound around the side face of the floor plate 2, andthe floor plate 2 is induction heated by means of the high-frequencymagnetic field generated by the high-frequency current. Furthermore, atrain detecting device 14 is disposed in front of a points section 13 inthe direction of travel of the trains, as indicated by the arrow in FIG.9C, and is connected via an inverter controller 15 to the inverterdevice 5. The inverter controller 15 inputs an approach signal when atrain has approached the points section 13, and after detecting this asan approach signal, for a prescribed period of time, it outputs a signalto the inverter device 5 whereby the supply of high-frequency current tothe heating coil 1 a is reduced or halted. By adopting thisconstruction, when a train passes over the points section 13, the effectof the high-frequency noise generated in the points section 13 on thehigh-precision equipment of the train is reduced.

(Tenth Embodiment)

A tenth embodiment of the invention is described with reference to FIGS.10A and 10B. In this embodiment, the train detecting device 14 asdescribed in the ninth embodiment is disposed on the central portion ofthe main rail 6. The train detecting device 14 is constituted by asignal generator 18 for generating a signal from the commercial powersource 3, a magnetic field detector 19 for converting an electricalsignal to a magnetic flux, and an amplifier 20 for amplifying thesignal. For the aforementioned magnetic field detector 19, a coil 19 agenerating a magnetic field is used. When a portion of a train wheel 17approaches, the magnetic resistance of the magnetic flux 16 produced bythe coil 19 a changes, and accordingly, the impedance of the coil 19 achanges. If the train detecting device 14 detects the approach of atrain due to a change in impedance, then the signal generator 18generates a signal and said signal is transmitted to the invertercontroller 15 via the amplifier 20. According to the train detectingdevice 14 of the present embodiment, the presence or absence of a trainis detected by means of a change in the impedance of the coil 19 a and achange in the signal current, due to change in the magnetic fieldaccording to whether or not a train is present. Thus, when a trainpasses over the points section, the effect of the high-frequency noisegenerated at the points section on the high-precision equipment of thetrain is reduced, by either reducing or interrupting the supply ofhigh-frequency current to the heating coil 1 a.

(Eleventh Embodiment)

An eleventh embodiment of the invention is described with reference toFIG. 11. In this embodiment, the thawing device for railway track pointshas the same basic construction as that in the first to eighthembodiments, and further includes the train detecting device 14 providedin front of the points section 13 in the direction of travel of thetrains, as indicated by the arrow in the Figure. More specifically, in aspecific section N comprising a prescribed distance of the railwaytrack, a transit path circuit is formed by the right and left rails 21and 22, and a signal generator 23 supplies an excitation signal from thecommercial power source 3 to a transit path relay 24, by means of atransit path transformer 25 and a resistor 26, when a train 27 entersinside the specific section N and the left and right rails 21 and 22 areshorted by a train axle 27 a, the excitation signal supplied to thetransit path relay 24 is reduced. A signal transmitter 28 is connectedto the transit path relay 24, a signal device 29 and a signal receiver30, and if it is judged from a change in the excitation signal suppliedto the transit path relay 24 that the train 27 is present inside thespecific section N, then the signal device 29 automatically operates andoutputs a train present signal to the signal receiver 30. In thisembodiment, the train detecting device 14 is constituted by the signalreceiver 30 and the signal transmitter 28. The inverter controller 15 isconnected to the train detecting device 14 and if it is judged that thetrain 27 is passing through, or has halted in the points section 13within the specified section N, then the controller outputs a signal tothe inverter device 5 whereby the supply of high-frequency current tothe heating coil 1 a is either reduced or interrupted. By adopting thisconstruction, the effect of high-frequency noise generated in the pointssection 13 on the high-precision equipment of the train is reduced.

INDUSTRIAL APPLICABILITY

According to the present invention, there is provided a thawing devicefor railway track points which has a good effect in preventing iceformation on floor plates, main rails and tongue rails, by high-powerinduction heating using high-frequency electric current, and which,furthermore, does not require removal outside of the snow season.

Moreover, by providing a protection against coil magnetism and aprotection against cable magnetism, leakage of high-frequency magneticflux generated in the heating coils and cables is reduced, therebyreducing the effect of high-frequency noise on other devices.

Furthermore, by providing a train detecting device, and implementingcontrol by an inverter controller whereby the supply of high-frequencycurrent from the inverter device to the heating coil is reduced orinterrupted for a prescribed period of time after the approach of atrain has been detected, the effect of high-frequency noise generated inthe points section on the high-precision equipment of the trains isreduced. Therefore, the thawing device for railway track pointsaccording to the present invention is beneficial in that it achievesheating of high efficiency by using high-frequency current, whilst alsosecuring safety by suppressing the effects of the magnetic flux causedby the high-frequency current on other devices and on the high-precisionequipment of the trains.

What is claimed is:
 1. A thawing device for railway track points,comprising: a heating coil (1 a) for heating a floor plate (2) byinduction; an inverter device (5) for supplying high-frequency currentto the heating coil (1 a); a train detecting device (14) for detectingthe approach of a train to a points section (13); and an invertercontroller (15) for outputting a signal, to the inverter device (5), thesignal for either reducing or interrupting the supply of high-frequencycurrent to the heating coil (1 a) for a prescribed period of time afterthe approach of a train has been detected by said train detecting device(14).
 2. The thawing device for railway track points according to claim1, wherein said train detecting device (14) comprises a magnetic fielddetector (19) for converting an electrical signal into a magnetic fluxand detecting changes in magnetic field caused by the approach of atrain.
 3. The thawing device for railway track points according to claim1, wherein said train detecting device (14) is constituted by a signaltransmitter (28) for inputting a track signal indicating whether shortcircuit is caused between left and right-hand rails (21, 22) by an axle(27 a) of a train (27) within a prescribed section, and transmitting atrain present/absent signal; and a signal receiver (30) for receivingthe train present/absent signal.
 4. A thawing device for railway trackpoints, comprising: a heating coil for heating a floor plate byinducting; and an inverter device for supplying high-frequency currentto the heating coil, wherein, the heating coil is wound through one ormore turns in contact with the lower face of the floor plate.
 5. Athawing device for railway track points, comprising: a heating coil forheating a floor plate by induction; and an inverter device for supplyinghigh-frequency current to the heating coil, wherein the heating coil iswound in contact with the side face of the floor plate and a portionthereof is wound in contact with the upper face of the floor plate.
 6. Athawing device for railway track points, comprising: a heating coilwound around a floor plate for heating said floor plate by induction; aninverter device for supplying high-frequency current to the heatingcoil; and a protection against coil magnetism for preventing magneticflux of the heating coil from leaking, wherein the protection againstcoil magnetism is constituted by closed loop conductors disposed aboutthe periphery of the heating coil.
 7. A thawing device for railway trackpoints, comprising: a plurality of heating coils wound around floorplates for heating the floor plates by induction; an inverter device forsupplying high-frequency current to the heating coils; a feeder cablefor connecting the heating coils in series; a supply and returnconnection cable for connecting the heating coils and the inverterdevice; and a protection against cable magnetism for preventing magneticflux of the cables from leaking, wherein said protection against cablemagnetism is constituted by twisting the supply and return connectioncables and the feeder cable.
 8. A thawing device for railway trackpoints, comprising: a plurality of heating coils wound around floorplates for heating the floor plates by induction; an inverter device forsupplying high-frequency current to the heating coils; a feeder cablefor connecting the heating coils in series; a supply and returnconnection cable for connecting the heating coils and the inverterdevice; and a protection against cable magnetism for preventing magneticflux of the cables from leaking, wherein said protection against cablemagnetism is constituted by cable magnetism-proof covers for coveringthe supply and return connection cables and the feeder cable, the coversbeing connected in a closed loop in the vicinity of the heating coilsand the inverter device.
 9. A thawing device for railway track points,comprising: a plurality of heating coils wound around floor plates forheating the floor plates by induction; an inverter device for supplyinghigh-frequency current to the heating coils; a feeder cable forconnecting the heating coils in series; a supply and return connectioncable for connecting the heating coils and the inverter device; and aprotection against cable magnetism for preventing magnetic flux of thecables from leaking, wherein said protection against cable magnetism isconstituted by superposing coils in which portions of the supply andreturn connection cables are wound respectively in the same direction,to the same diameter, and through the same number of turns.
 10. Athawing device for railway track points, comprising: a heating coil forheating a floor plate by induction; and an inverter device for supplyinghigh-frequency current to the heating coil, wherein the heating coil iswound with a portion thereof being in contact with the upper face of thefloor plate.
 11. A thawing device for railway track points, comprising:a heating coil for heating a floor plate by induction; and an inverterdevice for supplying high-frequency current to the heating coil, whereinthe heating coil is wound through one or more turns in contact with thelower face of the floor plate and a portion thereof is wound in contactwith the upper face of the floor plate.